1. Field of the Invention
The present invention relates to a nitride semiconductor light emitting diode.
2. Description of the Background Art
Japanese Patent Laying-Open No. 06-268257 proposes a structure in which an active layer includes multiple InGaN layers that are different in In (Indium) ratio.
Japanese Patent Laying-Open No. 10-084132 proposes a superlattice structure in which an active layer includes a quantum well layer and a barrier layer.
Japanese Patent Laying-Open No. 2006-060197 proposes a group III nitride semiconductor stack in which heavily doped layers and lightly doped layers are alternately stacked. The heavily doped layers are each a group III nitride semiconductor layer doped with n-type impurities of a relatively higher concentration, and the lightly doped layers are each a group III nitride semiconductor layer doped with n-type impurities of a relatively lower concentration.
As seen from above, conventional light emitting diodes as have been reported generally adopt the technique of the multiple quantum well structure as an active layer structure.
One of the factors of deterioration in luminous efficiency of a light emitting diode is deterioration in light extraction efficiency due to self absorption of an active layer. The structure of the active layer may be, for example, a multiple quantum well structure or single quantum well structure. The multi-quantum well structure is likely to be influenced by the self absorption, due to the fact that well layers in the active layer are different in the fluctuation in mixed crystal or the like as described above. As for the single quantum well structure, while the influence of the self absorption depends on the thickness of the layer, the single quantum well structure is less likely to be influenced by the self absorption. It is difficult, however, for the single quantum well structure to achieve high luminous efficiency as compared with the multi-quantum well structure.